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potatofrenzy | 2 years ago
Signals travel through traces. It's just that the motion of charges in the conductor is mediated by electromagnetic forces, and electric and magnetic fields are not constrained to the conductor. Indeed, electrochemical batteries aside, most of the energy storage in an electrical circuit is mediated by fields interacting with the surrounding space.
At low switching speeds, these effects are inconsequential outside discrete components specifically designed to exploit them (capacitors, inductors). At high speeds, these small capacitances and inductances begin to have perceptible effects, for example turning the PCB a non-negligible capacitor that induces voltages and currents on other layers.
A related problem is that when trace length is no longer negligible in function of wavelength, you can no longer treat signals as changing the potential across the entire conductor in an instant. You get different voltages in different places, and all of sudden, you have to worry about wave propagation - reflections, etc.
Some of the advice in this article isn't entirely sound; for example, you certainly don't need to worry about sharp trace angles or vias at 50 MHz. Similarly to the fetish of (often discontinuous!) ground planes, there's a lot of PCB design advice that matters in specific use cases (and even there, needs to be done well) that over time morphed into a bit of a "you absolutely need to do this in your Arduino project or else".
GeorgeTirebiter|2 years ago
If you click on the "Tech Tips" link on the left side of that page, you will get to his discussion of multi-layer PCBs. ("PCB Stackup").
Read This Section, and Become Enlightened! ;-)
jbay808|2 years ago